Diffraction microphone



Aug. 27, 1929. DE FOREST 1,726,289

DIFFRACTI 0N MI CROPHONE Filed Oct. 29, 1926 avwemtoz Patented Aug. 27, 1929.

uNiTEo STATES LEE DE FOREST, OF NEW YORK, N. Y., ASSIGNOR, BY MESN E ASSIGNMENTS, TO GEN- ERAL TALKING PICTURES CORPORATION, A CORPORATION OF DELAWARE.

mrrnacriou' mcaornona.

' Application filed October 29, 1926. Serial No. 144,977.

This invention relates broadly to micro-, phone construction whereby sound waves are converted into electrical current variations.

The microphone of my'invention relates to a device for transforming sound waves into light fluctuations, and in turn, translating said light fluctuations into electric currents.

Another object of my invention is the provision of a novel form of microphone which utilizes the diffracting power of two layers of 'difi'racting'media comprising one layer of air or gas at a different temperature and pressure than a contiguous layer.

A still further object of my invention is the provision'of an apparatus of this type which varies the light from a constant source by andin accordance with sound waves, which light waves are impressed upon a light sensitive cell, where they are converted into electrical current variations.

Another object of my invention is the ,pro-. vision of diifracting media adjacent to 'a polished reflecting surface for accomplishing the above transformation.

A still further object of this invention is the provision of means for heating a reflecting surface to provide adjacent diffracting media, for the purposes described above.

It is also a purpose of m invention to provide a diffracting microp one utlhzing diffracting media other than'air, such as vapors from volatile liquids. These and many other objects are success-. fully sought by the constructions disclos d herein, as embodying some of the possible forms of my invention.

The invention resides substantially in the combination, construction, arrangement and relative location of parts, as will appear more fully hereinafter.

Referring to the drawings,

Fig. 1 shows a diagrammatic view of one form of my invention, using a curved reflecting surface.

Fig. 2 is a diagrammatic view showing a cylindrical reflecting surface in crossl-section, utilizing the exterior of the cylinder as the reflecting surface. I

Fig. 3 represents a somewhat similar form in which a hollow cylinder, interrupted for part of its circumference, and polished on the inside, is used.

Fig. 4 represents another form of my invent1on, in which two segmental polished refleeting surfaces are shown in cross-section.

Fig; 5 represents a still further form of my invention, in which the beam of light from the light source falls upon a curved surface arranged relative to two mirror surfaces, the V curved surface being very thin 'and flexible. Fig. 6 represents a still-further modified form in which provision is made for 'supply- I ing a vapor from a volatile liquid to provide one of the difi'racting media.

It is well known that when a polished sure face is heated, the layer of air next to it becomes highly diffracting and possesses to an unusual degree the power to diffract light rays. The degree of diffraction possessed by such a layer of air depends upon the denlying next thereto. This density is a function of its temperature and pressure. I have discovered that sound waves ini inging upon such a succession of layers 0 air of varying densities, can, by varying the pressure or temperature of these layers, correspondingly effect their 'clifi'racting power. have therefore utilized this principle in constructing a microphone which utilizes a ray of light from a suitable source, which, when passed through such a layer of diifractin air, becomes moreor less diffracted, aroun the surface of the fleeting member. T e sound waves, by rapidly changing'the density of this layer, will cause thelight rays to penetrate with v'ary- I mg degree so as to influence, through a small aperture, a photo-electric cell or other light sensitive device.

olished'and heated re- "from the source 1 is confined to a relative ly thin band of light. This band is trans-' mitted through the set of lenses 3, where it is condensed so as to be projectedupon the curved polished surface 4. This polished surface, as well as those to be described later, may be made of any suitable material, for example, as silver, platinum, pyrex, glass, quartz, and the like: A source ofheat, such as the resistance coil 5, connected to a current source 5, may be used for heating the reflecting member 4 and theair' contiguous therewith. Here again it is evident that any suitable heating means may be used in any of the constructions disclosed. The light 70 sity of this layer and of the layer of air rays, after passing through the heated layer and being diffracted thereby, travel in a new 'rays on to the condensing lens system 9,

which may be of any form found useful for this purpose, from whence they are transmitted through the light aperture in the member 10, on tothe surface of the polished cylinder 11. A number of mirrors 12, placed the cylinders 11, but separated therefrom, are arranged parallel to a tanadjacent to gent plane, so that the light rays after passing through the layer rounding the cylinder 11, are diffracted or deflected so as to strike the first mirror 12. They are then reflected from this mirror back to the surface of the cylinder 11, and so on until they pass through the slot in the member 13, and then -finally' to the light sensitive device. 14,--wherethey are translated into varying electrical currents.

' As above, a suitable -heating. means 17, supplied from. a ower source 17, is disposed this time within the hollow cylinder ll'for heating it.

In the modification of Fig. .3, a light source 8, a condensing lens 9', and slit forming member 15, are provided asv before.

- However, in this construction the-cylinder 16 is hollow and polished onthe interior, 35

and has its surface interrupted to permit light to enter into the cylinder, where it is reflected from the polished surface of the cylinder and diffracted by the heated'air'so as chan e its direction a lurality of times, and is nally transmitted out through the opening in the cylinder and through the slit forming member 19 to the-light senstitive cell or device 20. I prefer to '--use a thin, dark gauz'e screen at each end of the cylinder 16, for the purpose of shutting out extra-neous light and air currents, and at the 'may be specially the same time, permitting sound waves to pass freely through 'the cylinder axially.

In the arrangement in Fig. 4, the light rays from the source are transmitted throu h the heated air betweentwo segmenta polished cylinders 22 and 23, which adjusted with respect to other suitable adjusting means 26. The heating coils 24 and 25.are providedfor heating olished surfaces of the segments. A slit ormin member 27 again confines the light to a t in band, and the light rays are transmitted to a dark chamber or supporting means 28, within which-any suitable light sensitive'cell may be disposed.

The arrangement of Fig. 5 is somewhat different, as will appear. The rays from the light source 29 pass through the lens system of heated air survolatile .in my invention, when desirable, this nature or any suitable vapors may be I heated air will, by cooling,

to the light sensitive cell as disclosed above.

30 and the slit forming member 31, and their large degree cut off by the surfaces of 33 and 34.

aperture in the member 35 sensitive cell 36.' y

In the arrangement in Fig. 6, the light ray strikes against the concave surface-of the member 41, which is heated by meansof the heating coil l2. A vapor from any suitable liquid, such as-alcohol, ether and the like, is; maintained adjacent to. the curved polished surface of 41,;and heated by contact therewith. A vessel 37 is shown-having the on to the light The remaining light is diffracted around the surface 36, passing finally through an liquid 39 therein, and a stopper 38 at one end. At the-other end is a porous sealing member 40, such as a, sponge, by means of which the liquid is gradually'evaported, and rises againstthe surface 41. I contemplate, vapors of used in connection with any of the modifications of my invention. The operation of the device, except that shown in Fig. 5, is as follows :When the air surrounding .the polished surface-is quiescent, the light from the source which falls on the light sensitive cell is constant. However, as soon as sound waves impinge upon or aredirected toward the polished heated surface, the layer of or by changes in density alternately diminlsh or increase the thickness of these layers, and thereby vary the amount of light passing therethrough by and in accordance with the sound waves ei'fectin the difi'racting power of the layer. It Wlll, of course, be evident that this operation occurs whether heated air is utilized as a diffracting medium, or other suitable vapors, such In the arrangement in F1g. 5, the sound waves impinge directly upon the thin curved surface, causing it to vibrate, and thus, by mechanical displacement, affecting the density of the air in contact with the surface to correspondingl vary the intensity of the li therethrough to the photo-e light sensitive cell. It would, of course, be evident that I could use a heatin .means in connection with the curved sur ace 32, in the arrangement of Fig. 5,.if. desired. From the foregoing description, it will be evident that I have devised a' very new and novel'form of microphone utilizing the prinectric or other struction and re ative rrangement of parts ht transmitted v will readily suggest themselves to those the inventive thought disclosed herein and recited in my appended claims. 1

What Iseek to secure by United States Letters Patent, is

1. In a device of the type described, the combination with a light sensitive means of a light source and a source of heat waves,

said heated waves. being adaptedto influence the light from said source by and in accordance with sound waves impinging upon said source of heat waves to cause the heat waves to change their physical characteristics.

2. In a device of the type and characteristics disclosed, the combination with a light actuated device of a source of constant illumination and means for varying the quantity of illumination falling on said device by and in accordance with sound waves said means including a body of heat waves.

3. In a device of the type and character.

disclosed, the combination with a light sensitive cell of means for producing a constant illumination, and a reflecting surface adjacent the path of said illumination, said surface having a layer of difiracting medium adjacent thereto and adapted to vary its diffracting power by and in accordance with sound waves to vary the quantity of illumination impinging on said cell. a I

4. In a device of the type and character disclosed, the combination with a light sensitive cell of means for producing a constant illumination, and a curved polished reflecting surface adjacent the nation, said surface having a layer of difpath of said illumifracting medium adjacent thereto and adapted to vary its diflracting power by and in accordance with sound waves to vary the qulantity of illumination impinging on said ce 1. J

5. In a diffraction-microphone, the combination of a light source with a polished surface, means for heating said surface to envelope it in a layer of heated air and a light sensitive cell adapted to receive light from said source varied by and in accordance with sound waves transmitted through the layer of heated air.

6. In a diffraction microphone the combination with a light source of a hollow reflecting body, means within for heating the surrounding gas, and a light actuated device, the light falling on said device bein varied by and in accordance with soun waves striking said heated gas.

7. In a'diffracti'on microphone, the combination with a light source of a hollow reflecting body having a light aperture and a polished interior surface, heating means within said body and a light actuated device arranged to receive the light from said source after passing into and out of said aperture.

8. In a diffraction microphone, the combination with a light source of a hollow reflecting body having a light aperture and a polished interior surface, electrical heating means within said body and a light actuated device arranged to receive the light from said source after passing into and out of said LEE m; FOREST. 

